1. Field of the Invention
This invention relates to a process for in-situ remediation of contaminated soils by the addition of certain treatment agents, such as chemicals to enhance mass transfer of pollutants from soils and non-aqueous phase liquids and to stimulate bacteria to degrade organic pollutants. More particularly, this invention relates to an improved method for the delivery of chemicals for enhancing bioremediation and for the physico-chemical separation and removal of pollutants from contaminated soil and groundwater whereby the pollutants are desorbed from the soil and non-aqueous phase liquids, such as tar and oil, and are available for biodegradation and/or physical removal from the soil by a mobile foam fluid phase. This invention also relates to a method for enhancing electrokinetic, electromagnetic and radio frequency (RF) in-situ treatment processes for in-situ treatment of inorganic and hydrocarbon pollutants in contaminated soils using foams.
2. Description of Prior Art
The conventional method for chemical enhancement of in-situ treatment of contaminated soils consists of the introduction of chemicals using hundreds of thousands of gallons of water into the soil subsurface using infiltration galleries. The main disadvantage of this technique is that the water carrier stream provides poor penetration into clay lenses and non-aqueous phase liquids and moves in a downward direction, due to gravity, into the underlying groundwater.
Subsurface contamination of soil is typically caused by spills or waste impoundments that have leaked over many years and have been observed at a variety of industry and government-owned facilities. Such sites include abandoned manufactured gas plants which release tars and polynuclear aromatic hydrocarbons (PAH's), creosote treatment sites which release tars, PAH's, and pentachlorophenol, spills at refineries which release oils and PAH's, gas dehydration facilities which release triethylene glycol and benzene, toluene, ethylbenzene and xylene, military bases, and oil and gas production pits. Cleanup of contamination in the deep subsurface, that is 4 or more feet below the surface of the soil, is cost-prohibitive to excavate and difficult to treat without considerable risk to the groundwater. As a result, there is a need to develop low-cost environmentally acceptable approaches for in-situ treatment.
Much work has been done in the past to develop various remediation approaches for the removal of pollutants from the soil subsurface such as in-situ bioremediation which has the potential for destroying pollutants in the subsurface at a low cost, for example, by the introduction of chemical enhancements such as Fenton's Reagent (iron/peroxide) and surfactants which promote biodegradation of pollutants in soils contaminated with non-aqueous phase liquids. In particular, surfactants and Fenton's Reagent are known to enhance the desorption of pollutants from the non-aqueous phase liquids and soil, thereby providing controlled solubilization of the pollutants, making them amenable to biological attack. See, for example, Kelley, R. L. et al., "Field-Scale Evaluation of an Integrated Treatment for Remediation of PAH's in Manufactured Gas Plant Soils," Institute of Gas Technology, Chicago, Ill.
The use of chemicals to enhance the desorption of pollutants from non-aqueous phase liquids and soil is also described in the literature for in-situ treatment. See, for example, Wunderlich, R. W., "In Situ Remediation of Aquifers Contaminated with Dense Nonaqueous Phase Liquids by Chemically Enhanced Solubilization," Journal of Soil Contamination, 1(4):361-37. Enhancement agents include nutrients, such as ammonia and orthophosphate, solvents, such as methanol and ethanol, and microbial cultures. Biological in-situ treatment occurs when nutrients, oxidants and other enhancements are added to the subsurface to stimulate bacteria in the subsurface to degrade organic pollutants. Various types of biological in-situ designs are discussed in the literature, for example Wunderlich et al. cited hereinabove and Sims, J. L. et al., "In Situ Bioremediation of Contaminated Unsaturated Subsurface Soils," USEPA Engineering Issue No. EPA/540/S-3/501, Robert S. Kerr Environmental Research Laboratory, Ada, Okla. It is believed that the enhancements reported in the literature for soil bioremediation are broadly applicable to the in-situ cleanup of a wide variety of industrial and the government sites. The challenge is in developing a method of delivering the chemical and biological enhancements for in-situ remediation of the subsurface without inadvertently contaminating the underlying groundwater or uncontaminated soils surrounding the contaminated site.
The Sims et al. reference cited hereinabove describes a number of delivery techniques currently in use including gravity infiltration and forced hydraulic delivery, the various designs of which include flooding, ponding, ditches, sprinkler systems, and subsurface injection techniques. All of these conventional methods for delivery of enhancement chemicals to the subsurface pose a considerable risk to groundwater because they involve the gravity flow of hundreds of thousands of gallons of chemical-bearing water streams that can move through contaminated regions of the subsurface, pick up considerable concentrations of pollutants and flow past non-aqueous phase liquids and clay lenses into the underlying and surrounding groundwater aquifers.
The primary problem with water-based delivery systems for chemicals transport in the subsurface is that gravitational forces have a dominating influence over the direction of flow of these fluids, thereby resulting in increased risk to groundwater. In contrast to water-based delivery systems, foam flow in porous media is not dominated by gravity but can be directed in the subsurface by differences of pressure and resistance to flow in the porous media. Aqueous foams are utilized in a number of applications, particularly in petroleum production. These include the use of foam for enhancement of oil recovery and as a selective blocking fluid in heterogeneous reservoirs. Foams are also known to be employed in near-well operations, such as sand clean-out, stimulation and sealing of the formation to control groundwater movement, or losses of injected fluids such as gas in underground gas storage reservoirs. Literature relevant to the application of foams to the recovery of oil from porous media is summarized in Nutt, C. W. et al., "The Influence of Foam Rheology in Enhanced Oil Recovery Operations," pp. 105-147, Foams: Physics, Chemistry and Structure, edited by A. J. Wilson, Spronger-Verlag, New York, N.Y. The technical feasibility of utilizing aqueous foams in porous media to mobilize a type of non-aqueous phase liquid for enhanced oil recovery which is performed more than 3,000 feet below the surface is generally disclosed by this body of literature. See also U.S. Pat. Nos. 5,203,413, 5,076,357, 5,074,358, 4,681,164, 3,953,338, and 3,707,193, all of which generally relate to the use of foams for enhancing oil recovery and/or for treating oil wells.
U.S. Pat. No. 3,822,750 teaches a method and apparatus for cleaning wells by forming a foamy aqueous solution at the bottom of the well and forcing a sand-bearing foamy aqueous solution with oil-bearing sand to the top of the well. U.S. Pat. No. 3,195,634 teaches a fracturing process for treating earth formations containing oil or gas deposits in which a composition comprising liquid carbon dioxide and an aqueous fluid as a fracturing fluid is injected as a liquid into the formation to be treated until maximum penetration has been achieved. Pressure at the well head is maintained until the desired action of the treating fluid in the formation has occurred in which the pressure is relieved causing the liquids previously injected into the formation to flow back into the well, liberating carbon dioxide gas in the formation as well as suspended in the aqueous fluid in the form of bubbles. The bubbles pick up residual oil and other matter as they are carried back into the well by an inflowing current of water. The liberated gas creates a gas lift to discharge a fracturing fluid from the formation and return the fracturing fluid to the surface, resulting not only in fracturing, but also cleanout of the formation.
U.S. Pat. No. 4,203,837 teaches foam flotation for removing particulates from waste water; U.S. Pat. No. 4,435,292 teaches a portable system for cleaning contaminated earth in which vertical and/or horizontal perforated pipes are imbedded in the soil around the contaminated area and connected in a closed portable system to a pressure pump in series with an evacuator having a separator and scrubber; U.S. Pat. No. 5,172,709 teaches an apparatus and process for removal of contaminants from soiled or other substrate materials by injection of a hot pressurized liquid, preferably steam, which vaporizes a fraction of the contaminant which is then released through a vapor filter to prevent atmospheric cross-pollution; U.S. Pat. No. 3,787,316 teaches a process for concentrating suspensions of activated sludge using a bubble flotation process in which foam is pumped into the suspension and the bubbles in the foam attach to the solids in the suspension, the air bubbles lifting the solids to which they have become attached and forming a blanket of concentrated sludge. Finally, U.S. Pat. Nos. 5,008,019 and 4,401,569 both relate to treatment of contaminated sites in conjunction with biodegradation. In-situ bioremediation of contaminated soils is also taught by U.S. Pat. No. 5,061,119 which teaches subsurface in-situ remediation by high pressure jet liquid injections of microorganisms, nutrients, etc., serving as a carrier to uniformly distribute treating agents in an underground treatment zone and withdrawal through an adjacent well; U.S. Pat. No. 4,850,745 which teaches bioremediation by placement of bacteria in soil at the bottom of a cavity for petroleum tanks and providing nutrients and air by way of a pipe; and U.S. Pat. No. 5,059,252 which teaches in-situ surface bioremediation by mixing a cation ion exchange resin with contaminated soil to promote growth of microorganisms capable of degrading hazardous waste.
The use of foams in agriculture is taught by U.S. Pat. Nos. 4,997,592, 3,891,571, 3,713,404, 3,373,009, 3,799,755, 3,417,171, and 3,466,873.
The successful application of aqueous foams to enhanced oil recovery suggests that foams can be effectively injected into the ground and used to affect the rheology and flow of non-aqueous phase liquids in the subsurface. However, foams used in the petroleum industry are designed for use at extremely high pressures, on the order of thousands of psi. Because high pressures tend to stabilize these foams, their use in shallow formations, where pollutants are located at contaminated sites, usually less than several hundred feet below the surface, results in a failure to maintain stable bubble formation. In addition, oil-production foam formulations are tailored in rheological properties to achieve specific tasks related to petroleum recovery or gas storage and, thus, are inappropriate for site remediation applications.
The use of foams for separation and transportation of chemicals is also known. Historically, interfacial separation by means of flotation has been known since the turn of the century. In particular, foam fractionation was used to remove sodium-oleate from an aqueous solution to verify the Gibbs adsorption equation. In addition, it has been demonstrated that a wide variety of substances can be removed from solution using flotation methods, which methods have been classified according to their function and application under the general heading of adsorptive bubble separation methods.
Adsorptive bubble techniques are divided into two main groups, foam separation and nonfoaming adsorptive bubble separation. Foam separation requires the generation of a foam for separation while nonfoaming separation does not require the generation of a foam.
Foam separation is further divided into two general categories: foam fractionation, which is the foaming off of dissolved material from a solution by means of adsorption at bubble surfaces, and froth flotation, which is the removal of particulate material by foaming. An example of the froth flotation technology is ore flotation which involves the separation of ore particles from gangue particles by selective attachment to rising bubbles. Other known froth flotation technologies include: macroflotation, the removal of macroscopic particles; microflotation, the removal of microscopic particles such as microorganisms and colloids; ion flotation, the removal of surface-active ions through the use of a surfactant which yields an insoluble product; precipitate flotation, in which a precipitate is removed and the precipitating agent is other than a surfactant; molecular flotation, in which surface-inactive molecules are removed through the use of a surfactant which yields an insoluble product; and adsorbing colloid flotation, the "piggy-back" removal of dissolved material which is first adsorbed on colloidal particles.
In the environmental field, the dissolved air flotation process which involves the dissolving of air in an influent water stream through contact with air in a high pressure chamber followed by a release of the stream into a shallow reaction chamber at atmospheric pressure which causes the release of fine gaseous bubbles from the water fraction, the bubbles impinging on particulate solids and the buoyant force of the combined particle and gas bubbles causing the particles to rise to the surface, has been used commercially for the separation of particulate solids in the treatment of water and waste water. This process is known to be widely effective for sludge treatment and for the treatment of algae-laden waters and low-turbidity, highly-colored waters.
Foam fractionation involves the selective adsorption of a surface-active solute onto the surface of gas bubbles rising through a dilute solution and forming a foam. The foam, when collected and collapsed, forms a concentrated solution of the surface-active solute which is removed from the bulk of the original dilute solution. In a laboratory-scale apparatus, foam fractionation has been used to perform a continuous separation for the purification of pulp and paper mill wastes. See Brasch, D. J. et al., "Rates of Continuous Foam Fractionation of Dilute Kraft Black Liquor," Separation Science and Technology, 14:6-70.